Tackle I had to make unyielding (5)
I believe the answer is:
rigid
'unyielding' is the definition.
(I've seen this in another clue)
'tackle i had' is the wordplay.
'tackle' becomes 'rig' (I've seen this in another clue).
'i had' becomes 'i'd' (contraction).
'rig'+'id'='RIGID'
'to make' acts as a link.
(Other definitions for rigid that I've seen before include "Stiff and inflexible" , "not relaxing" , "unwilling to move" , "starched too much?" , "stern" .)